1. Field of the Invention
The present invention relates to fluororubber compositions. More particularly, this invention relates to peroxide-curable fluororubber compositions exhibiting improved process-ability during roll milling and acceptable physical properties at temperatures below 0 degrees centigrade.
2. Background Information
Due to their excellent mechanical properties, heat resistance, oil resistance, and chemical resistance fluororubbers are used in a wide range of industrial applications. One shortcoming of this type of rubber is the poor workability or processability of curable compositions on roll-type rubber mills. In addition, cured fluororubbers typically exhibit relatively poor mechanical properties at temperatures below zero degrees Centigrade.
Japanese Patent Publication No. 59/227971, which issued on Dec. 21, 2984 discloses a friction material prepared by blending a silicone rubber, a fluororubber, a reinforcing fiber, a friction-imparting agent, a vulcanizing agent and a vulcanizing assistant. The resultant material is kneaded, rolled, frozen, and finally ground. The particles are then blended with other ingredients to form a paper.
Japanese Patent Publication No. 60/112431, published on Jun. 18, 1985 describes compositions suitable for use as the outer layer of a fixing roll in an electrostatic copier. The material used to form the layer is prepared by blending a curable silicone rubber with a dispersion of a fluororubber in a mixture of a silicone oil and either water or an organic liquid.
Japanese Patent Publication No. 61/72505, published on Apr. 14, 1986 teaches various compositions for preparing vulcanization bladders used during the vulcanization of rubber articles such as tires. One of the numerous compositions that can be used is a mixture of a silicone rubber and a fluororubber.
U.S. Pat. No. 4,810,577, which issued to Ikegaya on Mar. 7, 1989 discloses insulation materials for electrical wires that are blends of a vinylidene fluoride-based fluororubber and a silicone rubber. The silicone rubber reduces adhesion of the insulation material to the conductor without adversely affecting the oil resistance or mechanical strength of the fluororubber.
The present inventors have discovered that when a fluororubber is combined with an organopolysiloxane gum and an epoxy-substituted organoalkoxysilane the aforementioned shortcomings associated with cured and uncured prior art fluororubber compositions are eliminated without adversely affecting other desirable properties of the unmodified fluororubber. The present invention is based on this discovery.
An objective of this invention is to provide a fluororubber composition which prior to curing exhibits excellent workability on a roll mill and yields a cured rubber exhibiting acceptable low-temperature mechanical properties of the cured material.